DE102024205342A1 - Optical fiber for a display device - Google Patents

Abstract

The present invention relates to an optical fiber (400) for a display device (100) with a display panel (200). The optical fiber (400) has an input area (410) for coupling light (301) from a light source (300), wherein the input area (410) includes a collimator (411) for collimating the light (301). The optical fiber (400) also has a light guide area (420) for guiding the collimated light (301) along an axis (424), wherein the light guide area (420) has a top surface (421) that is parallel to the axis (424) and a bottom surface (422) that is inclined relative to the axis (424) and has a structure (423) for deflecting the collimated light incident on the bottom surface (422) towards the top surface (421). The structure (423) is designed to achieve a homogeneous, planar illumination of the top surface (421). The light guide (400) further comprises a deflection area (430) with a light deflection surface (431) for deflecting the collimated light into the light guide area (420), wherein the deflection surface (431) is arranged at an angle (α) of 45° to the orientation of the collimated light (301) and to the axis (424) of the light guide area (420), and the light deflection surface (431) has a structure (432).

Description

The present invention relates to a light guide for a display device for installation in a motor vehicle. Such light guides for backlighting a display of a display device are used nowadays in almost every motor vehicle, for example in a speedometer.

Display backlights are most often based on light guides into which light from multiple light-emitting diodes (LEDs) is coupled. The light propagates through the light guide by total internal reflection and is then re-extended by microstructures on the light guide, resulting in a homogeneous light distribution. This design enables very compact and efficient display illumination with a wide beam angle.

With such backlighting applications, it is often necessary to deflect the light by 90° after coupling it into the optical fiber. This deflection is typically achieved using a planar or curved deflection surface. In both cases, the light emitted by the LED is coupled in planarly, meaning the emitted light strikes a planar coupling surface of the optical fiber. With both designs, the deflection area must be obscured to prevent stray light.

Using a curved deflection surface generally allows for high deflection efficiency. The efficiency increases with the degree of curvature of the deflection surface.

A disadvantage of this approach is that as efficiency increases, the coverage width also increases, which is undesirable in many applications. If deflection needs to be implemented in a small space, the previously described concepts result in efficiency losses of 50% or more.

Against this background, he describes US 2014/0003071 A1 An optical device for a motor vehicle, comprising a light source and a light guide designed to direct light from the light source into a beam with substantially parallel rays. A collimator focuses the light rays emitted by the light source to produce the beam with substantially parallel rays. A reflective surface inclined at 45° deflects the beam by 90°. A series of further reflective surfaces inclined at 45° serve to deflect the beam again for light extraction. The light exits the light guide by means of refractive elements in the surface of the light guide. The optical device is used to implement elements of a motor vehicle's exterior lighting system.

The present invention is based on the objective of providing an improved solution for homogeneous backlighting of a display device in which a compact light deflection is realized.

This problem is solved according to the invention by a light guide for a display device according to the preamble of independent claim 1 together with the features of the characterizing part of independent claim 1. Advantageous embodiments can be found in the dependent claims.

The invention provides a light guide for a display device with a display panel, wherein the light guide has an input area for coupling light from a light source, wherein the input area has a collimator for collimating the light, wherein the light guide has a light-guiding area for guiding the collimated light along an axis, wherein the light-guiding area has a top surface that is designed parallel to the axis and a bottom surface that is inclined relative to the axis and has a structure for deflecting the collimated light incident on the bottom surface towards the top surface, wherein the structure is designed to achieve a homogeneous, planar illumination of the top surface, wherein the light guide has a deflection area with a light-deflection surface for deflecting the collimated light into the light-guiding area, wherein the light-deflection surface is arranged at an angle of 45° to the orientation of the collimated light and to the axis of the light guide area, and wherein the light-deflection surface has a structure.

In the solution according to the invention, the light guide is designed to collimate the light emitted by a light source, e.g., an LED, at least approximately. The collimated light rays then strike the light deflection surface at defined angles, thereby significantly reducing the formation of stray light. The structured light deflection surface ensures that a uniform, homogeneous illumination of the light guide area is achieved. Light deflection using a collimator can achieve more than 80% efficiency in a very small space. The unusable edge of the display panel can thus be reduced to just a few millimeters, enabling the realization of virtually borderless displays.

A particular advantage of the optical fiber according to the invention is that the structure of the light deflection surface has a roughness that ensures the reflected light is spread out and light from different light sources mixes. This avoids areas of varying brightness and results in particularly homogeneous illumination in the optical fiber area.

According to an advantageous embodiment of the invention, the light deflection surface has a structure with a roughness in the range of 1.1 µm to 2.2 µm, preferably a roughness of 1.1 µm. It has been found that a roughness in this range ensures particularly homogeneous light mixing and homogeneous light distribution in the light guide area. With a structure that preferably has a roughness of 1.1 µm, the desired area illumination of the light guide area and thus homogeneous backlighting of the display panel can be easily achieved.

According to an advantageous embodiment of the invention, the coupling area between the collimator and the deflection area has a second light deflection surface. Because the collimator generates essentially parallel light rays, the distance between the collimator and the deflection area can be adapted to the specific design of the display device, i.e., the height of the light guide can be varied. This height variation is particularly advantageous in instrument clusters with integrated display panels. A further advantage is that the second light deflection surface also deflects light rays that are not fully collimated into the light guide area, thus reducing light loss.

According to an advantageous embodiment of the invention, the second light-deflection surface has a structure with a roughness in the range of 1.1 µm to 2.2 µm, preferably a roughness of 1.6 µm. It has been found that a roughness in this range ensures a particularly good reduction of light loss.

According to an advantageous embodiment of the invention, the light guide has a third light deflection surface between the deflection area and the light-guiding area. An advantage is that light rays that are not fully collimated are deflected into the light-guiding area, thus reducing light loss.

According to an advantageous embodiment of the invention, the third light-deflection surface has a structure with a roughness in the range of 1.1 µm to 2.2 µm, preferably a roughness of 1.6 µm. It has been found that a roughness in this range ensures a particularly good reduction of light losses and homogeneous light mixing in the optical fiber area.

According to an advantageous embodiment of the invention, the third light-deflection surface has a radius between 1.5 mm and 2.5 mm, preferably a radius of 2 mm. An advantage is that a curved surface in the area of the third light-deflection surface ensures improved homogenization with only a slight loss of efficiency. It has been found that a radius of 2 mm is particularly advantageous.

According to an advantageous embodiment of the invention, the light guide has at least one chamfer at the coupling area and/or the deflection area, which forms a fourth light deflection surface.

In the preferred case, the optical fiber has a chamfer on two opposite sides, the left and right sides, at the coupling and deflection regions, respectively. Alternatively, a chamfer can be formed on only one side of the optical fiber, or only at the coupling region or only at the deflection region.

One advantage is that the chamfer at the coupling and deflection points creates a compact light guide design, resulting in a smaller installation space requirement. This allows for compact and efficient light deflection in a small area. Another advantage is that the chamfer at the coupling and deflection points creates an additional, and more importantly, wider light deflection area than the light coupling area compared to a conventional design with edges.

According to an advantageous embodiment of the invention, the fourth deflecting surface has a structure with a roughness in the range of 1.1 µm to 2.2 µm, preferably a roughness of 1.6 µm. It has been found that a roughness in this range ensures a particularly good reduction of light loss.

According to an advantageous embodiment of the invention, at least two single-color LEDs are provided as the light source. Such an embodiment is useful if the light guide is to be used for backlighting a display panel that is not backlit by a single light source. An advantage is that the use of different colored single-color LEDs and the inventive roughness of the light-reflecting surfaces results in the production of a desired homogeneous light color. Particularly white light can be achieved when light sources with a suitable base color are used.

It has been found that, for example, the combination of red (R-LED), green (G-LED), and blue (B-LED) LEDs, also known as R/G/B-LEDs, is particularly well-suited. Using R/G/B-LEDs allows for excellent coverage of white light, as well as any color desired by the customer, and color correction. A further advantage is that replacing a colored LED with one of a different color eliminates the need to measure new LEDs, making the use of R/G/B-LEDs both time- and cost-efficient.

The optical fiber according to the invention is used in display devices, particularly in the automotive sector, e.g. for a central display in the dashboard or a combination instrument.

Further features of the present invention will become apparent from the following description and the attached claims in conjunction with the figures. Advantageous embodiments of the invention will also become apparent from the features of the following description and the figures.

To better understand the principles of the present invention, embodiments of the invention are explained in more detail below with reference to the figures. The same reference numerals are used in the figures for identical or equivalently acting elements and are not necessarily described again for each figure. It is understood that the invention is not limited to the embodiments shown and that the described features can also be combined or modified without departing from the scope of protection of the invention as defined in the appended claims.

Figure overview

• 1 bekannte Konzepte zur Lichtumlenkung in einem Lichtleiter.
• 2 einen Schnitt durch eine Ausführungsform eines erfindungsgemäßen Lichtleiters;
• 3 eine Schrägansicht einer Ausführungsform eines erfindungsgemäßen Lichtleiters;
• 4 eine Schrägansicht einer Ausführungsform eines erfindungsgemäßen Lichtleiters mit mehreren Lichtquellen am Einkoppelbereich;
• 5 einen Schnitt durch eine Anzeigevorrichtung mit einem erfindungsgemäßen Lichtleiter.

They show, in a schematic, sketch-like representation:

• 1 known concepts for light deflection in a fiber optic cable.
• 2 a section through an embodiment of an optical fiber according to the invention;
• 3 an oblique view of an embodiment of a light guide according to the invention;
• 4 an oblique view of an embodiment of an optical fiber according to the invention with multiple light sources at the coupling area;
• 5 a section through a display device with a light guide according to the invention.

Character description

1 This shows known concepts for light deflection in an optical fiber 400. In backlighting applications, it is often necessary to deflect the light 301 by 90° after coupling it into the optical fiber 400. In one concept, a planar deflection surface 431 is used for this deflection. This concept is shown in 1a ) is shown and achieves a deflection efficiency of approximately 50%. In another concept, a curved surface 431 is used for deflection. Examples of this are in 1b) and 1c ) shown. In 1b) The curved surface 431, or the section through the curved surface 431, is a circular arc. In 1c In contrast, the deflection is parabolic. In all cases, the light emitted by a light-emitting diode 301 (not shown in the figure) is coupled in planarly; that is, the emitted light 301 strikes a planar coupling surface of the optical fiber 400. In both concepts, the area of the deflection surface 301 must be obscured due to stray light.

When using a curved deflection surface 431, a high deflection efficiency can generally be achieved. The efficiency increases the smaller the curvature of the deflection surface. For example, while in the 1b) The arrangement shown only achieves an efficiency of 40%; the efficiency of the arrangement shown is in 1c The arrangement shown is at 90%. However, this means that with increasing efficiency, the width of the coverage becomes ever larger, which is undesirable in many applications.

2 Figure 1 shows a section through an exemplary embodiment of an optical fiber 400 according to the invention. The optical fiber 400 has an input area 410 for coupling light 301 from a light source 300, e.g., a single-color LED. The input area 410 has a collimator 411 for collimating the light 301. The collimator 411 can be based, at least partially, on total internal reflection.

In an exemplary embodiment, the coupling area 410 further comprises a groove 417 as a coupling surface in the collimator 411, wherein the groove 417 has several coupling surfaces, in this exemplary embodiment three, aligned with each other. In the assembled state, the light source 300 is arranged with the light guide 400 below the groove 417 of the collimator 411. The coupling of the light 301 emitted by the light source 300, i.e., the emitted light 301, strikes the individual coupling surfaces. The surfaces of the groove 417 and the emitted light 301 are coupled into the coupling area 410. The mutually aligned surfaces of the groove 417 are polished.

A light guide area 420 serves to guide the collimated light along an axis 424. The light guide area 420 has a top surface 421, which is parallel to the axis 424, and a bottom surface 422, which is inclined relative to the axis 424. The bottom surface 422 has a structure 423 for deflecting the collimated light incident on the bottom surface 422 towards the top surface 421. The structure 423 is designed to provide planar illumination of the top surface 421. The structure 423 can be, for example, a mirror structure or a grating structure, such as a reflection grating. The structure 423 is formed on the outside of the bottom surface 422 of the light guide area 420.

A deflection area 430 with a light deflection surface 431 serves to deflect the collimated light into the light guide area 420. The light deflection surface is arranged at an angle α of 45° to the orientation of the collimated light 301 and to the axis 424 of the light guide area 420. Preferably, the light deflection surface 431 is planar. The light deflection surface 431 has a structure 432 such that a homogeneous light distribution is achieved in the light guide area 420. The structure 432 is a microstructure or, for example, a mirror structure or a grid structure. The structure 432 is formed on the outside of the light deflection surface 431 of the deflection area 430.

Since the collimator 411 essentially generates parallel light rays, these rays strike the light deflecting surface 431 at nearly identical angles when a planar light deflection surface 431 is used. Parallel light rays then propagate within the light guide area 420, the advantage of which lies in the predictable propagation behavior. The structure 432 ensures that the light rays reflected into the light guide area 420 are expanding beams that overlap each other, thus achieving a planar, homogeneous illumination of the light guide area.

In 2 For clarity, the coupling area 410 and the deflection area 430 are shown larger than necessary for the actual realization of the light guide 400. Between the collimator 411 (or the coupling area 410) and the deflection area 430, the light guide 400 has a second light deflection surface 412 with a structure 413 for deflecting the collimated light so that even light rays that are not fully collimated are deflected into the light guide area. The structure 413 is a microstructure, such as a mirror structure or a grid structure. The structure 413 is formed on the outside of the light deflection surface 412. Because the collimator 411 essentially generates parallel light rays, the distance between the collimator 411 and the deflection area 430 can be adjusted to the specific design of a display device by adapting the second light deflection surface 412, i.e., the height of the light guide 400 can be varied.

Furthermore, the light guide 400 has a third light deflection surface 425 with a structure 426 between the deflection area 430 and the light guide area 420. The structure 426 improves the uniform, homogeneous illumination of the light guide area. In preferred embodiments, the third light deflection surface 425 has a radius r, which deflects light rays that are not completely collimated into the light guide area 420 of the light guide 400. The location of the radius r is shown in the present figure, but its value is so large in the section plane shown here that no curvature is discernible.

3 Figure 1 shows an oblique view of an embodiment of an optical fiber 400 according to the invention. The optical fiber 400 is largely identical to the one described in Figure 2. 2 The optical fiber 400 shown in the figure has a chamfer 414 on two opposite sides, the left side and the right side of the optical fiber 400, in the coupling area 410 and in the deflection area 430, respectively. The chamfer 414 preferably has an angle of 45°. The chamfer 414 on each side forms a fourth light deflection surface 415 with a structure 416 for deflecting the collimated light into the light-guiding area. The structure 416 is a microstructure, or for example, a mirror structure or a lattice structure. The structure 416 is formed on the outside of the fourth light deflection surface 415. In the upper part of the figure, a curvature of the light deflection surface 415, which is denoted here by radius r, can be seen. The coupling surfaces of the coupling area 410 formed in the groove 417, as well as the collimator 411 formed in this area, are different from the previous illustration. 2 The collimator 411 and the coupling surfaces of the coupling area 410 formed in the groove are arranged at an angle to each other, allowing for a smaller coupling area as a usable area. The individual coupling surfaces have different angles and radii relative to each other. as well as different sizes of the individual surfaces.

4 Figure 1 shows an oblique view of an optical fiber 400 according to the invention with several light sources 300 arranged in the coupling area 410 for backlighting a display panel (not shown). For this purpose, light from several individual light sources 300, also referred to as single-color LEDs, preferably configured as R/G/B LEDs, arranged side by side in a row, is coupled in. The optical fiber 400 preferably has an assigned area of the coupling area 410 for each individual light source 300. The individual light sources 300 are arranged alternately in the colors red (R-LED), green (G-LED), and blue (B-LED) below the groove 417.

At the in 4 In the solution shown, the light guide 400 uses a common light deflection surface 431 or a common deflection area 430 as well as a common light guide area 420 for all coupling areas 410.

5 Figure 1 shows a cross-section through a display device 100 with a light guide 400 according to the invention in the assembled state. In this embodiment, the light source 300, whose light 301 is to be distributed by the light guide 400, is arranged on a circuit board 500 of the display device 100. The light 301 emitted by the light source 300 is coupled into the light guide 400 in the coupling area 410 and deflected by means of the deflection area 430 into the light guide area 420. There, it is deflected towards the top of the light guide 400, where, after exiting the light guide 400, it serves to backlight a display panel 200.

Overall, the example shows how the invention can be used to create a simple light guide so that homogeneous light mixing occurs in the light guide with a small installation space requirement.

Reference symbol list

100

Display device

200

Display panel

300

light source

301

Light

400

optical fibers

410

Coupling area

411

Collimator

412

Second light deflection surface

413

structure

414

bevel

415

fourth light deflection surface

416

structure

417

Nut

420

Light guide area

421

Top

422

bottom

423

structure

424

axis

425

Third light deflection surface

426

structure

430

Deflection area

431

light deflection surface

432

structure

500

Circuit board

α

angle

r

radius

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• US 2014/0003071 A1 [0006]

Claims (10)

Light guide (400) for a display device (100) with a display panel (200), wherein the light guide (400) has a coupling area (410) for coupling light (301) from a light source (300), wherein the coupling area (410) has a collimator (411) for collimating the light (301), wherein the light guide (400) has a light guide area (420) for guiding the collimated light (301) along an axis (424), wherein the light guide area (420) has a top surface (421) that is configured parallel to the axis (424) and a bottom surface (422) that is inclined relative to the axis (424) and has a structure (423) for deflecting the collimated light incident on the bottom surface (422) towards the top surface (421), wherein the structure (423) is configured to be homogeneous to achieve area illumination of the top surface (421), wherein the light guide (400) has a deflection area (430) with a light deflection surface (431) for deflecting the collimated light into the light guide area (420), wherein the deflection surface (431) is arranged at an angle (α) of 45° to the alignment of the collimated light (301) and to the axis (424) of the light guide area (420), characterized in that the light deflection surface (431) has a structure (432). Optical fiber (400) to Claim 1 , characterized in that the light deflection surface (431) has a structure (432) with a roughness in the range of 1.1 µm to 2.2 µm, preferably a roughness of 1.1 µm. Optical fiber (400) according to one of the previous Claims 1 and 2 , characterized in that the coupling area (410) between the collimator (411) and the deflection area (430) has a second light deflection surface (412). Optical fiber (400) after the previous Claim 3 , characterized in that the second light deflection surface (412) has a structure (413) with a roughness in the range of 1.1 µm to 2.2 µm, preferably a roughness of 1.6 µm. Optical fiber (400) according to one of the previous Claims 1 until 4 , characterized in that the light guide (400) has a third light deflection surface (425) between the deflection area (430) and the light guide area (420). Optical fiber (400) after the previous Claim 5 , characterized in that the third light deflection surface (425) has a structure (426) with a roughness in the range of 1.1 µm to 2.2 µm, preferably a roughness of 1.6 µm. Optical fiber (400) according to one of the previous Claims 5 and 6 , characterized in that the third light deflection surface (425) has a radius (r) between 1.5 mm and 2.5 mm, preferably a radius (r) of 2 mm. Optical fiber (400) according to one of the previous Claims 1 until 7 , characterized in that the light guide (400) has at least one chamfer (414) at the coupling area (410) and/or the deflection area (430), which forms a fourth light deflection surface (415). Optical fiber (400) after the previous Claim 8 , characterized in that the fourth deflection surface (415) has a structure (416) with a roughness in the range of 1.1 µm to 2.2 µm, preferably a roughness of 1.6 µm. Optical fiber (400) according to one of the previous Claims 1 until 9 , characterized in that at least two single-colour LEDs are provided as the light source (300).